PN Junction Diode:Pin Diagram:

Circuit Symbol:

Circuit Diagram:Forward Bias:

Reverse Bias:

EXNO: DATE:

CHARACTERISTICS OF PN JUNCTION DIODE

Aim:(i) To plot the forward and reverse VI characteristics of PN junction

diode (Silicon diode) and calculate its cut – in voltage, static resistance and dynamic resistance.

Apparatus Required:

S. No.

Components Specification

Quantity

1. Silicon PN diode

1N4007 1

2. Voltmeter 0-20 V 13. Ammeter 0-200 mA 14. Ammeter 0-200 µA 15. Power Supply 0-30 V / 2A 16. Bread board - 17. Connecting

Wires- As

necessary

Formula Used: Change in Voltage ΔV Dynamicesistance, Rd =

Resulting Change in Current ΔI

Tabulation:Forward Bias:

Reverse Bias:

Forward VoltageVf (V)

Forward CurrentIf (mA)

Model Graph:

Reverse VoltageVr (V)

Reverse CurrentIr (µA)

Theory:PN Diode:

When a P – type and an N – type semiconductor are joined together, a junction diode is created. It has the unique ability to allow current only in one direction. The lead connected to the P – type semiconductor is called anode and that connected to the N – type is called cathode. The P – type and N – type semiconductors are electrically neutral before the junction is formed. As soon as the junction is formed, the majority carriers are trying to diffuse through the junction. This happens due to the concentration gradient of holes and electrons existing inside the diode. Due to the diffusion of majority carriers from P – region to N- region and vice – versa, neutrality ends and a potential barrier forms across the junction. The barrier potential is 0.6 V for Silicon. The region thus created is due to the majority carriers. It has a depth of about 1 µm and is called depletion region.(i) Forward Bias:

If the anode of the diode is connected to the positive terminal of a battery and cathode to the negative terminal, the set up is called forward bias. The diode does not pass any current till the battery voltage exceeds the potential barrier. Once the battery potential exceeds the barrier potential, high forward current in the order of mA flows through the diode due to the movement of holes and electrons.(ii) Reverse Bias:

When the positive terminal of a battery is connected to the N – type and negative terminal is connected to the P – type, the diode is said to be

reverse biased. This connection makes the majority carriers in the semiconductor move away from the junction. So the depletion region gets more widened. The minority carriers move towards the junction and cause a minute current flow through the diode which is in the order of µA in Germanium diodes and nA in Silicon diodes.(iii) Static and Dynamic Resistances of the Diode:

When the diode is forward biased, it offers a definite resistance in the circuit. The static resistance or DC resistance is the ratio of DC voltage across the diode to the DC current flows through it. Dynamic resistance or AC resistance of the diode at any point is the reciprocal of the slope of the tangent of the characteristic curve at that point.

Change in Voltage ΔV

Dynamic Resistance = = Resulting Change in Current ΔI

Procedure:For PN Junction Diode:

1. The circuit is set up on breadboard keeping the supply voltage at the minimum position (say 0V).

2. The supply voltage is varied so that the voltmeter readings vary from 0 to 0.7 V or 0.8 V in steps of 0.1 V. Take the readings of voltmeter and ammeter and enter it in the tabular column for the forward bias connection.

3. For reverse bias connection, the input voltage is varied from 0 to 10V in steps of 1V and enters the ammeter and voltmeter readings.

4. To measure forward static resistance, consider a point on the forward characteristics and note the corresponding voltage and current. The ratio of voltage to current is the static resistance. To measure reverse static resistance, repeat this step by considering another point on reverse characteristics.

5. To measure dynamic forward resistance, for a particular DC current, find out the reciprocal of the slope at the point corresponding to that current. It is extremely high because the slope is almost zero.

Questions for Discussion:1. Define peak inverse voltage of a diode.2. Why Silicon diodes are more popular than Germanium diodes?3. What do you mean by ‘1N’ in 1N4007?4. Differentiate Zener and Avalanche breakdown.5. Write down the applications of PN Junction and Zener diodes.

Result:(i) Thus the forward and reverse VI characteristics of PN diode are

plotted and the following parameters are obtained.a) Cut – in Voltage of PN junction diode =____________ V.b) Dynamic Forward Resistance at 10 mA=_____________Ω.c) Static Forward Resistance at 10 mA =_____________Ω.

CIRCUIT DIAGRAMHalf Wave Rectifiers

0.000 V+

-

20.0026 Vpk 60 Hz 0° vi

2kΩR

DIODE_VIRTUAL

A B

G

T

Half Wave and Full Wave rectifiersAIMTo obtain the characteristics of half wave and Full wave rectifier circuits.APPARATUS REQUIRED

DIODE_VIRTUAL

169.706 Vpk 60 Hz 0° vi

1kΩR

A B

G

T

SL.NO

Equipment /Component Type/Range Quantity

1 CRO 30 MHz 12 Transformer 12-0-12 13 Signal Generator (0-30 MHz 14 Diode 1N4007 25 Resistors 1 k, 2 k Each 16 Bread Board - 1

THEORYAn electrical device which offers a low resistance to the current in one direction but a high resistance to the current in the opposite direction is called a rectifier. Rectifier is capable of converting a sinusoidal input waveform, whose average value is zero into unidirectional waveform, with a nonzero average component. A diode is usually used as the rectifying device. Half wave rectifier is one converts the ac to dc in one half of the cycles only. Full wave rectifier is one which converts the ac to dc in both the positive and negative half cycles.

PROCEDURE1. Design the circuit by following the design procedure.2. Simulate the circuit using Multisim.3. Test the circuit functions.4. Connect the circuit as per the circuit diagram given.5. Observe the circuit output and compare with simulation

output.

Full Wave Rectifier

169.706 Vpk 60 Hz 0° vi

DIODE_VIRTUALD1

DIODE_VIRTUALD2

1kΩR

T1

0 1:2

A B

G

T

Half Wave Rectifier output

GRAPH SHEET

Half Wave Rectifier output

Full Wave Rectifier output

REFERENCES1. ‘Electronic Devices and Circuits ‘ Millman, halkias,

Satyabratajit, Tata McGraw Hill . ( page nos 177-187 )2. ‘Electronic Devices and Circuits ‘ David A . Bell, PHI ( page

nos 52-64 )3. ‘Electronic Devices and Circuit Theory ‘ Robert L. Boylested ,

Loius Nashesky. PHI ( page nos 76-83 )

QUESTIONS FOR DISCUSSION1. Why are rectifiers used with a filter at their output?2. Define voltage regulation of a rectifier?3. What is the ideal value of regulation?4. What does no-load condition refer to?5. What are the advantages of a bridge rectifier?6. What are the advantages and disadvantages of a capacitor filter?7. What are the applications of rectifiers?8. What is the regulation of r a (i) Half - wave circuit (ii) Full-wave circuit9. What is PIV? State it is value in case of (i) Half wave (ii) Full wave (iii) Bridge rectifier.RESULTThe Half-Wave and Full-Wave rectifier circuits were designed and simulated; the characteristics curve was plotted in each case.

Pin Diagram:

Circuit Symbol:

Circuit Diagram:

EXNO: DATE:

CHARACTERISTICS OF COMMON EMITTER CONFIGURATION

Aim:To plot the input and output characteristics of an NPN transistor in

common emitter configuration and to find out the dynamic input resistance, dynamic output resistance and common emitter current gain.

Apparatus Required:

S. No.

Components Specification Quantity

1. RPS (0 – 30) V 12. Ammeters (0 – 200)mA, (0 –

200 )µA Each 1

3. Voltmeter (0 – 20) V 24. Resistor 1 KΩ 15. Transistor BC 107 16. Bread Board - 17. Connecting

Wires- As

necessary

Theory:Transistor can be connected in a circuit in any one of the three

different configurations namely common emitter, common base and common collector. In this configuration input is applied between base and emitter, and output is taken from collector and emitter. Here, emitter of the transistor is common to both input and output circuits and hence the name common emitter configuration. It is also called grounded emitter

configuration. The bias voltage forward biases the base-emitter junction and Vcc is used to reverse bias the collector-base junction. The input voltage in the CE configuration is the base-emitter and the output voltage is the collector-emitter voltage. The input current is IB and the output current is Ic.

Tabulation:Input Characteristics:

VCE = V VCE = V VCE = VVBE

(V)IB

(µA)VBE

(V)IB

(µA)VBE

(V)IB

(µA)

Output Characteristics:

IB = µA IB = µA IB = µAVCE

(V)IC

(mA)VCE

(V)IC

(mA)VCE

(V)IC

(mA)

For audio frequency applications common emitter is used. Common emitter is the most frequently used configuration because it provides voltage, current and power gain always greater than unity.(i) Dynamic Input Resistance (ri):

Dynamic input resistance can be calculated from the input characteristic curves. It is given by the ratio of small change in base to emitter voltage to corresponding change in base current, keeping collector to emitter voltage constant.

ri = VBE/IB keeping VCE constant.(i) Dynamic Output Resistance (rO):

Dynamic output resistance can be calculated from the output characteristic curves. It is given by the ratio of small change in collector to emitter voltage to corresponding change in collector current, keeping base current constant.

ro = VCE/IC keeping IB constant.(iii) Common Emitter Current Gain ():

It is the ratio of the change in collector current to the corresponding change in base current, keeping the collector to emitter voltage constant.

= IC /IB keeping VCE constant.Procedure:Input Characteristics:

1. The circuit connections are made as shown in figure.2. Keeping the VCE as 0 V, the input voltage VBE is varied from 0 to 0.8

V in step of 0.1 and the corresponding input current IB is noted.3. Step 2 is repeated for several values of output voltage VCE (Say

3V, 6V, etc.).4. All the readings are tabulated.

5. The V-I characteristics curve is plotted by taking VBE along X – axis and IB along Y axis for each value of VCE.

6. The dynamic input resistance is calculated by taking the ratio of change in VBE to the resulting change in IB at any point (say 10 µA), which is the inverse of the slope of the tangent of a curve at that point.

Model Graph:Input Characteristics: Output Characteristics:

Calculations:(i) Dynamic Input Resistance, ri = VBE/IB

(ii) Dynamic Output Resistance, ro = VCE/IC

(iii) Common Emitter Current Gain, = IC /IB

Output Characteristics:1. The circuit connections are made as shown in figure.2. Keeping the input current IB as 0 µA, the output voltage VCE is

varied from 0 to 10 V in steps of 0.5 V and the corresponding output current IC is noted until it becomes zero.

3. Step 2 is repeated for several values of the input current IB (say 50 µA, 100 µA).

4. All the readings are tabulated.5. The V-I characteristics curve is plotted by taking the output

voltage VCE along X – axis and output current IC along Y – axis for each value of IB.

6. The dynamic output resistance is calculated by taking the ratio of change in VCE to the resulting change in IC at any specific point on the curve, say 10 mA.

7. The common emitter current gain is calculated by using the formulae.

Questions for Discussion:1. What are the regions of operation of a transistor? Mention its uses.2. Why CE configuration is preferred as a switch?3. What is indicated by B, C and 107 in BC 107?4. Why common collector stage is also called as an emitter follower?5. Mention the importance of CE amplifier.

Result: Thus the input and output characteristics of an NPN transistor in CE

configuration is plotted and the following parameters are calculated.

a) Dynamic Input Resistance, ri =_____________Ω.b) Dynamic Output Resistance, ro =_____________Ω.c) Common Emitter Current Gain, =_____________.

Pin Diagram:

Circuit Symbol:

Circuit Diagram:

EXNO: DATE:

CHARACTERISTICS OF COMMON BASE CONFIGURATIONAim:

To plot the input and output characteristics of an NPN transistor in common base configuration and calculate its dynamic input resistance, dynamic output resistance and common base current gain.

Apparatus Required:

S. No.

Components Specification Quantity

1. RPS (0 – 30) V 12. Ammeters (0 – 100)mA 23. Voltmeter (0 – 1) V, (0 – 30)

VEach 1

4. Resistors 1 KΩ, 10 KΩ Each 15. NPN Transistor BC 107 1

6. Bread Board - 17. Connecting

Wires- As

necessary

Theory:

In common base configuration base of the transistor is common to both input and output circuits and hence the name common base configuration. Here the input is applied between emitter and base, and output is taken between collector and base. CB configuration is also called as Grounded base configuration. An increase in emitter current causes an increase in collector current. The bias voltage forward biases the base-emitter junction and Vcc is used to reverse bias the collector-base junction. The input voltage in the CB configuration is the emitter-base voltage and the output voltage is the base-collector voltage. The input current is IE and the output current is IC.

The transistor offers low input resistance and very high output impedance when it is in CB configuration. It provides almost unity current gain and high voltage gain.

Tabulation:Input Characteristics:

VCB = V VCB = V VCB = VVEB

(V)IE

(mA)VBE

(V)IB

(mA)VBE

(V)IB

(mA)

Output Characteristics:

IE = mA IE = mA IE = mAVCB

(V)IC

(mA)VCB

(V)IC

(mA)VCB

(V)IC

(mA)

(i) Dynamic Input Resistance (ri):Input characteristics are plotted between emitter current IE and the

emitter to base voltage VEB for a constant value of collector to base voltage VCB. The reciprocal of the slope of the curves gives the value of Dynamic input resistance ri.

ri = VEB/IE keeping VCB constant.(i) Dynamic Output Resistance (rO):

Output characteristics are plotted between collector current IC and the collector to base voltage VCB for a constant value of emitter current IE. Dynamic output resistance rO is obtained from these curves. It has rather high value since the curves are almost flat.

ro = VCB/IC keeping IE constant.(iii) Common Base Current Gain ():

It is the ratio of the change in collector current to the corresponding change in emitter current, keeping the collector to base voltage constant.

= IC /IE keeping VCB constant

Procedure:

Input Characteristics:1. The circuit connections are made as shown in figure.2. Keeping the VCB as 0 V, the input voltage VEB is varied from 0 to 0.8

V in step of 0.1V and the corresponding input current IE is noted.3. Step 2 is repeated for several values of output voltage VCB (Say

3V, 6V, etc.).4. All the readings are tabulated.5. The V-I characteristics curve is plotted by taking VEB along X – axis

and IE along Y axis for each value of VCB.6. The dynamic input resistance is calculated.

Output Characteristics:

1. The circuit connections are made as shown in figure.2. Keeping the input current IE as 0 mA, the output voltage VCB is

varied from 0 to 10 V in steps of 0.5 V and the corresponding output current IC is noted until it becomes zero.

3. Step 2 is repeated for several values of the input current IE (say 50 mA, 100 mA).

4. All the readings are tabulated.

Model Graph:Input Characteristics: Output Characteristics:

Calculations:(i) Dynamic Input Resistance, ri = VEB/IE

(ii) Dynamic Output Resistance, ro = VCB/IC

(iii) Common Base Current Gain, = IC /IE

5. The V-I characteristics curve is plotted by taking the output voltage VCB along X – axis and output current IC along Y – axis for each value of IE.

6. The dynamic output resistance and common base current gain is calculated by using the formulae.

Questions for Discussion:1. What are the applications of the CB amplifier?2. Which configuration is good as a constant current source? Why?

3. What is collector power dissipation of a transistor?4. Why the emitter of a transistor is highly doped and the area of

collector is made large?5. What does the arrow in the symbol of a transistor indicates?

Result:Thus the input and output characteristics of an NPN transistor in CB

configuration is plotted and the following parameters are calculated.a) Dynamic Input Resistance, ri =_____________Ω.b) Dynamic Output Resistance, ro =_____________Ω.c) Common Base Current Gain, =_____________.

Pre – lab test (20) Remarks

& Signature with Date

Simulation (20)Circuit connection (30)Result (10)Post-lab test (20)Total (100)

Pin Diagram:

Circuit Symbol:

Circuit Diagram:

EXNO: DATE:

CHARACTERISTICS OF COMMON COLLECTOR CONFIGURATION

Aim:To plot the input and output characteristics of an NPN transistor in

common collector configuration and calculate its dynamic input resistance, dynamic output resistance and common base current gain.

Apparatus Required:

S. No.

Components Specification Quantity

1. RPS (0 – 30) V 12. Ammeters (0 – 100)mA 23. Voltmeter (0 – 1) V, (0 – 30)

VEach 1

4. Resistors 1 KΩ, 10 KΩ Each 15. NPN Transistor BC 107 16. Bread Board - 17. Connecting

Wires- As

necessary

Theory:

In common collector configuration collector of the transistor is common to both input and output circuits and hence the name common collector configuration. Here the input is applied between collector and base, and output is taken between collector and emitter. CC configuration is also called as Grounded collector configuration. The bias voltage forward biases the base-collector junction and VEE is used to reverse bias the Base-emitter junction. The input voltage in the CC configuration is the coleector-base voltage and the output voltage is the emitter-collector voltage. The input current is IB and the output current is IE.

The transistor offers high input resistance and low output impedance when it is in CC configuration. It provides high current gain and low voltage gain.

Tabulation:Input Characteristics:

VEC = V VEC = V VEC = VVBC

(V)IB

(mA)VBC(V

)IB

(mA)VBC

(V)IB

(mA)

Output Characteristics:

IB = mAIB = mA

IB = mA

VEC

(V)IE

(mA)VEC

(V)IE

(mA)VEC

(V)IE

(mA)

(i) Dynamic Input Resistance (ri):Input characteristics are plotted between base current IB and the

collector to base voltage VBC for a constant value of collector to emitter voltage VEC. The reciprocal of the slope of the curves gives the value of Dynamic input resistance ri.

ri = VBC/IB keeping VEC constant.(i) Dynamic Output Resistance (rO):

Output characteristics are plotted between emitter current IE and the collector to emitter voltage VEC for a constant value of base current IB. Dynamic output resistance rO is obtained from these curves. It has rather high value since the curves are almost flat.

ro = VEC/IE keeping IB constant.(iii) Common collectro Current Gain ():

It is the ratio of the change in emitter current to the corresponding change in base current, keeping the collector to emitter voltage constant.

= IE /IB keeping VEC constant

Procedure:

Input Characteristics:

7. The circuit connections are made as shown in figure.8. Keeping the VEC as 0 V, the input voltage VBC is varied from 0 to 0.8

V in step of 0.1V and the corresponding input current IE is noted.9. Step 2 is repeated for several values of output voltage VEC (Say 3V,

6V, etc.).10.All the readings are tabulated.11.The V-I characteristics curve is plotted by taking VBC along X – axis

and IB along Y axis for each value of VEC.12.The dynamic input resistance is calculated.

Output Characteristics:

7. The circuit connections are made as shown in figure.8. Keeping the input current IB as 0 mA, the output voltage VEC is

varied from 0 to 10 V in steps of 0.5 V and the corresponding output current IE is noted until it becomes zero.

9. Step 2 is repeated for several values of the input current IB(say 50 mA, 100 mA).

10.All the readings are tabulated.

Model Graph:Input Characteristics: Output Characteristics:

Calculations:(i) Dynamic Input Resistance, ri = VBC/IB

(ii) Dynamic Output Resistance, ro = VEC/IE

(iii) Common Base Current Gain, = IE/IB

11.The V-I characteristics curve is plotted by taking the output voltage VEC along X – axis and output current IE along Y – axis for each value of IB.

12.The dynamic output resistance and common base current gain is calculated by using the formulae.

Questions for Discussion:6. What are the applications of the CC amplifier?7. Which configuration is good as a constant current source? Why?8. What is collector power dissipation of a transistor?9. Why the emitter of a transistor is highly doped and the area of

collector is made large?10.What does the arrow in the symbol of a transistor indicates?

Result:Thus the input and output characteristics of an NPN transistor in CC

configuration is plotted and the following parameters are calculated.a) Dynamic Input Resistance, ri =_____________Ω.b) Dynamic Output Resistance, ro =_____________Ω.c) Common Base Current Gain, =_____________.

EXNO: DATE:

CHARACTERISTICS OF JFET

Aim:To plot the VI characteristics of a Junction Field Effect Transistor.

Apparatus Required:

S. No.

Components Specification Quantity

1. RPS (0 – 30) V 22. Ammeter (0 – 500) A, (0 – 10)

mAEach 1

3. Voltmeter (0 – 10) V, (0 – 30) V Each 14. Resistor 220 Ω 25. JFET BFW11 16. E-MOSFET IRE5.6 17. D-MOSFET IRE5.6 18. Bread Board - 19. Connecting

Wires- As

necessary

Parameters Used For Calculation:Drain Characteristics: Dynamic resistance (rD) = ∆VDS / ∆ ID Tran conductance (gm) = ∆ ID / ∆VDS

Transfer Characteristics: Input resistance (Ri) =VGS / IDSS

Amplification factor (µ) = [∆VDS / ∆VGS] ID constant.

Tabulation:Transfer Characteristics:

Theory: FET is a three terminal semi conductor device in which conduction is due to any one type of majority carriers. So it is also called unipolar device. The three terminals are Source, Drain and Gate. The current conduction is controlled by the electric field between the gate and the conducting channel and hence the name FET.

VDS= VDS=

VGS (V) ID (mA) VGS (V) ID (mA)

Depending on the construction, the FET can be classified into two types. 1. N-Channel FET 2. P- Channel FETN-Channel FET: It consists of n-type silicon bar forming the conducting channel for the charge carriers. The heavily doped P regions introduced on both sides of the bar forms the gate. This is used to control the flow of electrons from source to drain. The majority carriers are electrons which cause the current flow.P- Channel FET:

It consists of p-type silicon bar forming the conducting channel for the charge carriers. The heavily doped N region introduced on both sides of the bar forms the gate. This is used to control the flow of electrons from source to drain. The majority carriers are holes which cause the current flow.

Procedure:1. Connections are given as per the circuit diagram.2. Gate to source voltage is reverse biased.3. When the voltage is applied between the gate and source (VDD) the

electrons flow from source to drain and this constitutes the drain current ID.

4. The value of drain current will be maximum, when there is no external voltage applied between gate and source; this current is designated as IDSS.

Transfer Characteristics:1. Keep a constant value for VDS.2. Adjust the gate-source voltage (VGS) and note down the ID value.3. For various VDS values, note down the values of VGS and ID.4. Plot a graph between VGS along Y-axis and ID along X-axis.

Drain Characteristics:

VGS(V) VGS(V)

VDS(V) ID(mA) VDS(V) ID(mA)

Drain Characteristics:1. Adjust gate to source voltage (VGS) to zero volt.2. Increase VDS and note down the corresponding ID value.3. Plot the graph for VDS along X-axis and ID along Y-axis.4. Similarly by placing various values for VGS=1,2,3……..plot the

curve and obtain the drain characteristics.

Questions for Discussion:1. Why a FET is said to be a voltage controlled device? 2. Why FET is called so?3. What is pinch – off voltage?4. Compare a FET with a BJT.5. How a FET functions as a voltage variable resistor?

Result: Thus the characteristic of JFET was studied and its curves were

plotted. The following parameters are calculated.(i) Drain Dynamic Resistance, rd = _______________ Ω.(ii) Mutual Conductance, gm = _______________.(iii) Amplification Factor, = _______________.

Unijunction Transistor:Pin Diagram: Circuit Symbol:

Circuit Diagram:

Model Graph:

EXNO: DATE:

CHARACTERISTICS OF UJT Aim:

(i) To plot the VI characteristics of a Unijunction transistor and to measure its intrinsic stand off ratio.

(ii) To study and plot the VI characteristics of SCR.Apparatus Required:

S. No.

Components Specification

Quantity

1. RPS (0 – 30) V 12. Ammeters (0 – 10)mA 23. Voltmeter (0 – 20) V 24. Resistor 1 KΩ 25. Resistor 3.2 KΩ 16. UJT 2N2426 18. Bread Board - 19. Connecting

Wires- As

necessary

Theory:Unijunction Transistor (UJT):

A Unijunction transistor consists of a highly doped N-type semi conductor bar to which a heavily doped P-type rod is attached. Ohmic

contacts are made at opposite ends of the N- type bar, which are called base-1(B1) and base-2 (B2) of the transistor. P-type rod is called the emitter (E). UJT is a three terminal semiconductor switching device. It has a unique characteristic that, when it is triggered, the emitter current increases and it is powered by the emitter power supply.

The inter base resistance RBB of the N-type silicon bar appears as two resistors RB1 and RB2, where RBB equals the sum of RB1 and RB2.

Tabulation:

VB1B2 = V VB1B2 = VIE

(mA)VEB1

(V)IE

(mA)VEB1

(V)

Calculation:

Intrinsic Stand off ratio, = (VP - VD)/VB1B2

The intrinsic stand off ratio is given by,

= RB1/RBB with IE = 0

Due to the applied voltage at B2 of the transistor, a positive voltage developed across RB1 equal to VBB. When VE < Voltage across RB1, diode becomes reverse biased. When VE increases, a forward current flows through the emitter to B1 region. If VE is raised further, a sudden reduction of RB1 occurs. This happens since increase in current reduces RB1 due to the negative coefficient of resistance of the semiconductor. A regenerative action takes place at a particular value of VE called the Peak voltage. After a valley point, IE increases with VE similar to ordinary forward biased diode.

When VE raises, the forward resistance across the junction decreases and the junction acts as short circuit. The current through EB1 junction increases and the voltage across the junction decreases. This continues up to a voltage called valley voltage VV after which the junction acts as an ordinary diode.

Silicon controlled rectifier:

The SCR is a four layer PNPN device and has three terminals namely anode (A), cathode (K) and gate (G). Keeping the gate open, if the forward voltage is applied across the SCR, it will remain in OFF state. If the applied voltage exceeds the break over voltage, it will turn ON and heavy current will flow through it. The break over voltage can be reduced if a small voltage is applied at the gate. As gate current increases, the break over voltage decreases. Once the SCR is fired, the gate loses control over the current through the device. Even if the gate circuit is disconnected, the anode current can not be brought back to zero. To turn OFF SCR, anode current should be made less than the holding current.

SCR is a unidirectional power switch and is being extensively used. It is a unique ac and dc rectifying element, rectifying ac to give controlled dc output and controlling dc to ac etc. SCR combines the features of the rectifier and a transistor. It can be used as a switch to perform various functions such as rectification, inversion and regulation of power flow.

Procedure:

Unijunction transistor:

1. The circuit connections are given as per the diagram.2. Keeping VBB = 0V, VE is varied from 0 to 10 V in steps of 0.5V and

the voltmeter and ammeter readings at the input side are noted.3. The above step is repeated for different values of VBB (say 3V,6V).4. The VI characteristic is plotted with IE along X-axis and VE along Y-

axis keeping VBB as constant and the intrinsic stand off ratio is calculated from the graph.

Questions for Discussion:1. Which region is called cut – off in UJT?2. Write the applications of UJT

Result:(i) Thus the VI characteristic of UJT is plotted and the intrinsic stand

off ratio is calculated as = _____________

.Circuit Diagram:

EX.NO: Date:

DIFFERENTIAL AMPLIFIER

AIM:To construct and study the performance of Differential Amplifier

using BJT and also calculate the Common mode gain, differential gain and CMRR and also plot the characteristic curve.

APPARATUS REQUIRED:

S.NO

COMPONENTS NAME RANGE TYPE QUANTITY

1. Function generator 5 MHz - 12. Resistor3. Transistor - - 2

THEORY:An amplifier which amplifies the difference between the two

input signals is called the differential amplifier. It is also called difference amplifier.

DIFFERENTIAL GAIN AD :The Ad is the gain with which differential amplifier amplifies the

difference between two input signals. Hence it is called differential gain of the differential amplifier.

COMMON MODE GAIN AC :

If we apply two input voltages which are equal in all the respects to the differential amplifier i.e V1 = V2 then ideally the output voltage Vo = ( V1 – V2 ) Ad, must be zero.

COMMON MODE REJECTION RATIO ( CMRR ) :

When the same voltage is applied to both the inputs, the differential amplifier is said to be operated in a common mode configuration. Many disturbance signals, noise signals appear as a common input signal to both the input terminals of the differential amplifier. Such a common signal should be rejected by the differential amplifier. The ability of a differential amplifier to reject a common mode signal is expressed by a ratio called Common Mode Rejection Ratio denoted as CMRR.

Procedure:

1. Connections are given as per the circuit diagram.2. Apply the input voltages (Vin1 and V in2) to the bases of the two

transistors.3. Obtain the output at the collector of the two transistors.4. Calculate the differential mode gain and common mode gain.5. Draw the characteristic curve.

Tabulation:

S.No Vs1 Ic1 Vs2 Ic2

RESULT:Thus the differential mode gain, common mode gain were

calculated and the characteristic curve of the BJT Differential amplifier were plotted.